I'm sorry for my late response but I have been away working so my bot has been standing a while but now I will take it up again. I will rewrite the hole PID part for my bot and also give it two separate PID controls for each motor that will try to keep a exact speed coming from a fuzzy logic control. Check my blog or here for updates..

The balancing robot for dummies guidehttp://www.x-firm.com/?page_id=145